Unconventional superconductivity in Na₀.₃₅CoO₂·1.3D₂O and proximity to a magnetically ordered phase

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Muon spin relaxation (μSR) measurements on the new layered cobalt oxide superconductor Na₀.₃₅CoO₂·1.3H₂O and its parent, non-superconducting compounds, have revealed unconventional nature of superconductivity through: (1) a small superfluid energy which implies a surprisingly high effective mass of the charge carriers, approximately 100 times the bare electron mass; (2) the superconducting transition temperature Tc scaling with the superfluid energy following the correlations found in high-Tc cuprate and some other two-dimensional superconductors; (3) an anisotropic pairing without broken time-reversal symmetry; and (4) the proximity of a magnetically ordered insulating phase at Na₀.₅CoO₂ below Tₙ = 53 K.